In industries such as the semiconductor industry, gases that are extremely toxic for human bodies, such as arsine (AsH.sub.3), phosphine (PH.sub.3) and boron trifluoride (BF.sub.3), are widely used for various objects, such as an ion implantation process in manufacturing of semiconductors. As a typical example of such an industrial use, arsine is conveniently supplied in containers such as cylinders containing either pure arsine or a mixture of arsine and a balance gas, such as hydrogen or helium. Leakage of arsine from the cylinders is a latent source of extreme danger particularly during the transportation and shipment of the cylinders. In order to solve the problem, a method is disclosed, for example, in U.S. Pat. No. 4,744,221, in which arsine is adsorbed to zeolite, which is a porous crystalline aluminum silicate, and stored at a negative pressure. According to this method, when the arsine once adsorbed to zeolite under a negative pressure is desorbed from the zeolite in a reversible reaction and delivered to the desired location, the danger of the toxic arsine diffusing into the atmosphere can be avoided by the negative pressure.
However, as arsine adsorbed to zeolite undergoes resolving at room temperature into arsenic and hydrogen, the concentration of pure arsine that can be extracted is decreased, and with the passage of time, the internal pressure of the canister increases due to the generation of hydrogen and becomes, in some cases, a pressure higher than the atmospheric pressure, resulting in danger of arsine leaking outside.
In order to avoid such danger, PCT WO96/11739 discloses that activated carbon containing less impurities is suitable for the storage of gaseous compound used as an ion implantation gas in the semiconductor industry, such as arsine, phosphine and boron trifluoride. However, since general activated carbon is produced from natural substances, such as coconut shell and coal, when pores are formed during an activation process, which is one step in the production process of activated carbon , the pore size distribution is broadened due to the influence of impurities contained in the raw material unevenness in composition and structure of the raw material, resulting in that it is not suitable for adsorptive storage of the particular gaseous compound in a high efficiency. Furthermore, since there are lot-to-lot differences in the raw material due to the difference in production district and production season, it is difficult to strictly control the pore size distribution contributing the adsorption capacity of the gas.
When activated carbon granules packed in a container do not have sufficient strength, there is a possibility that the activated carbon granules rub against each other or against the container wall due to the pressure change on transportation of the container and on adsorption and desorption of the gaseous compound. Such rubbing brings about deterioration of the activated carbon forming fine particles of carbon in the container, and a problem arises in that the fine particles of carbon clog a gas filter through which the gaseous compound is taken out from the container.
Activated carbon originated by a natural source contains various metals as impurities. When the activated carbon is used for adsorptive storage of gaseous compound such as arsine and phosphine as impurities are contained, the adsorbed gaseous compound undergoes resolving as similar to the case where zeolite is used as the adsorbent, for example, arsine is decomposed into arsenic and hydrogen as shown in the following scheme. EQU AsH.sub.3.fwdarw.As+3/2H.sub.2
By this resolution, the concentration of pure arsine that can be extracted is decreased, and furthermore with the passage of time, the internal pressure of the container increases due to the generation of hydrogen, and in some cases, it rises from the initial negative pressure to a pressure higher than the atmospheric pressure, resulting in danger of an extremely toxic gas such as arsine leaking outside.
In order to avoid such danger, the purity of activated carbon is heightened by washing with an acid such as hydrochloric acid, nitric acid, phosphoric acid and sulfuric acid. However, by conducting acid washing, an anion of the substance used for the acid washing may remain in the activated carbon , and when such activated carbon is used for adsorptive storage of arsine or phosphine, nitrogen gas or oxygen gas are generated due to reduction of the anion, which brings about problems of decrease in purity of the stored gas and leakage of the gas as similar to the cases described above.
In the case where high-purity activated carbon produced from a high-purity raw material is used, the problem of resolution of arsine into arsenic and hydrogen, for example, can be solved. However, even the high-purity activated carbon reacts with a gas such as arsine to generate impurities such as hydrogen, nitrogen, carbon monoxide and carbon dioxide. The thus generated impurity gases generally do not raise the gas pressure in the storage container to a pressure exceeding the atmospheric pressure, as different from the hydrogen gas generated by the resolution of arsine, and there is less danger of leakage to the outside in this point of view. However, the required purity of arsine, phosphine and boron trifluoride, which are used for the ion implantation process in the semiconductor industry for example, is at least 99.9% according to the SEMI International Standards (1990), and the reduction in purity of these gases may greatly deteriorate the value of these gases.
In the case where the particular gaseous hydrogenated compound and halogenated compounds used for production of semiconductors, which have been stored by adsorption under temperatures of the general working circumstances, are withdrawn by a vacuum pump to be desorbed and delivered with controlling its flow amount for practical use, the gaseous compounds finally remain in the container in not a little amount, and thus the amount of the gaseous compound that can be effectively used is limited.
Gaseous organic compounds, such as methane, which attract the attention of people as an environmental friendly energy source are stored in cylinder as high pressure gas or as liquefied gas. However, as the demand of the usage of the gaseous organic compounds is increased, it will become necessary for gas providers to make the storage method of the gas much more efficient and easy to use.